In the manufacture of an electronic device such as a semiconductor device, a plasma processing is performed on a processing target object by using a plasma processing apparatus. In general, the plasma processing apparatus includes a processing vessel, a gas supply system, a first electrode, a second electrode, a first high frequency power supply and a second high frequency power supply. The gas supply system is configured to supply a processing gas into the processing vessel. The first electrode and the second electrode are disposed with a space within the processing vessel therebetween. The first high frequency power supply is configured to generate a first high frequency power and supply the first high frequency power to either one electrode of the first electrode and the second electrode. The second high frequency power supply is configured to generate a second high frequency power having a relatively low frequency and supply the second high frequency power to the second electrode. Generally, in the plasma processing performed in this plasma processing apparatus, the processing gas is supplied into the processing vessel from the gas supply system, and the first high frequency power from the first high frequency power supply is supplied to the either one electrode. Accordingly, plasma of the processing gas is generated within the processing vessel. Further, the second high frequency power from the second high frequency power supply may be supplied to the second electrode when necessary.
As disclosed in Patent Document 1, for example, there is a plasma processing in which two separate stages of generating plasma of different processing gases are performed alternately. In this kind of plasma processing, when transitioning from a preceding stage to a succeeding stage, the processing gas supplied from the gas supply system is changed. Further, the second high frequency power is supplied to the second electrode only at the succeeding stage.
Since a gas has a mass, there is required a time period from a time point when the processing gas supplied from the gas supply system is changed to a time point when the processing gas within the processing vessel is actually changed. Meanwhile, the second high frequency power is supplied to the second electrode without any substantial delay. Accordingly, it happens that the second high frequency power is supplied to the second electrode before the processing gas within the processing vessel is changed. To solve this problem, in the plasma processing described in Patent Document 1, the supply of the second high frequency power is not begun until it is confirmed from a detection result of an emission spectrum within the processing vessel that the processing gas for the succeeding process has reached the processing vessel.
Patent Document 1: Japanese Patent Laid-open Publication No. 2013-058749
However, there may be no detectable difference between an emission spectrum of plasma of a processing gas used in a preceding stage and an emission spectrum of plasma of a processing gas used in a succeeding stage. In such a case, it may be difficult to accurately detect a time point when the processing gas is changed within the processing vessel. As a result, the second high frequency power may not be supplied to the second electrode at an appropriate timing.
Thus, in a plasma processing of generating plasma of different processing gases within the processing vessel in sequence, it is required to change a setting of a high frequency power at an appropriate time point after the processing gas supplied by the gas supply system is changed.